1. Field of the Invention
The present invention relates to a toner feeder and, more specifically, to a toner feeder for supplying toner to a developing device of an image forming apparatus.
2. Description of the Related Art
A toner feeder of the prior art related to the present invention is adapted to read information recorded on a bar code attached to a peripheral surface of a toner container bottle by an optical sensor to detect the specifications of the toner container bottle (see, for example, Japanese Unexamined Patent Publication No. 2001-235936).
Image forming apparatuses such as a copying machine, a facsimile machine and a printer utilizing an electrophotographic system typically include a photosensitive drum on which an electrostatic latent image is formed by laser irradiation means or the like, and a developing device provided in the vicinity of the photosensitive drum for developing the electrostatic latent image with toner. In such an image forming apparatus, a toner feeder (toner cartridge) is removably mounted for supplying the toner to the developing device.
Where the developing device employs a two-component developing agent containing a toner and a carrier such as iron powder, for example, the toner and the carrier are stirred to be homogeneously mixed in a stirring chamber, and the resulting two-component developing agent is transported to the vicinity of a developing roller incorporating a magnetic member.
The developing agent transported to the vicinity of the developing roller is carried on a surface of the developing roller by a magnetic field of the developing roller to provide a so-called magnetic brush. When the magnetic brush is brought into opposed relation to the photosensitive drum, only negatively charged toner is transferred onto the photosensitive drum to develop the electrostatic latent image. When the carrier separated from the toner thereafter passes through a repulsive magnetic field of the developing roller, the carrier falls back into the stirring chamber of the developing device.
Therefore, the toner concentration of the developing agent in the developing device is gradually reduced during repeated image formation. The reduction of the toner concentration is detected by a sensor provided in the developing device. In response to the detection, a toner hopper in which the toner is preliminarily stirred for easy mixing of the toner with the developing agent is driven to supply the toner to the developing device. When the toner concentration is recovered to a predetermined concentration level, the driving of the toner hopper is stopped.
When the amount of the toner in the toner hopper is reduced to less than a predetermined level, the reduction of the toner amount is detected by a sensor provided in the toner hopper, and a developing agent feeder is driven. That is, a toner container bottle is rotated to supply toner into the toner hopper from a toner outlet port thereof. When the toner is supplied to the predetermined level, the driving of the developing agent feeder is stopped.
The amount of the toner in the toner container bottle is also reduced during repeated supply of the toner. When the toner container bottle is substantially emptied, a message for replacement of the toner feeder is displayed on an operation panel of the image forming apparatus or the like to prompt a user to replace the toner feeder.
In order to prevent residual toner from leaking from the toner outlet port in the replacement of the toner feeder, the toner feeder generally has a shutter of a certain configuration provided on the toner outlet port.
The rotational position of the toner container bottle at which the toner container bottle is stopped after having been rotated by the driving of the toner feeder is not particularly defined. Therefore, the toner container bottle is often stopped with its toner outlet port oriented downward with respect to a gravity direction.
In this case, a pressure is exerted on toner present around the shutter, so that the toner is liable to be partly agglomerated. The agglomeration of the toner causes an excess load when the toner feeder is actuated, and results in poor toner supply and malfunction of the shutter.
If the shutter malfunctions, the toner leaks from the toner output port during demounting and mounting of the toner feeder, so that not only the inside of the image forming apparatus but also user's hands and the installation site of the image forming apparatus are contaminated with the toner.
The demounting and mounting of the toner feeder is required not only when the toner container bottle is emptied but also when a trouble such as a paper jam occurs. In this case, a great amount of toner remains in the toner container bottle, so that the malfunction of the shutter inevitably results in severe contamination.
The toner feeder disclosed in the aforesaid patent publication is capable of reading information on the bar code attached to the peripheral surface of the toner container bottle by the optical sensor to detect the specifications of the toner container bottle, particularly, to determine whether or not the toner container bottle is a genuine product. However, the toner feeder is incapable of stopping the toner outlet port at a specific rotational position.
It is also conceivable to detect timing at which the bar code passes by the optical sensor for stopping the toner outlet port at a specific rotational position at which no load is exerted on the shutter. However, the optical sensor is susceptible to contamination with scattered toner. If the bar code and the optical sensor are contaminated with the scattered toner, malfunction will occur.
It is also conceivable to provide cleaners for removing the scattered toner from the bar code and the optical sensor. However, the construction of the toner feeder is complicated, thereby resulting in poor reliability and cost increase.